A strip of film is incrementally advanced in a camera to position an unexposed frame relative to an exposure gate for exposure. The accurate advancement and registration of each frame relative to the exposure gate is critical to ensure correct frame-to-frame spacing and avoid an overlap of exposed images.
Various ways have been employed to meter a filmstrip. A common practice of achieving accurate metering is to utilize perforations disposed in the filmstrip, which can be detected to determine the correct positioning for a frame. A well-known conventional system uses a mechanical claw or pawl that detects a perforation corresponding to a next frame, and establishes registration for that frame when the perforation reaches a desired stopping point. Once registration is achieved, it is desirable to provide means to maintain the registration until the advancement of the filmstrip to the next frame so that the filmstrip does not creep out of alignment.
U.S. Pat. No. 4,746,943 relates to a film tracking mechanism having a track and a tracking member moving in a cyclic manner to engage and advance a filmstrip. While such a film tracking mechanism may have achieved a certain degree of success in its particular application, a need continues to exist for a metering apparatus which provides for the thrusting (i.e., initial positioning) of the filmstrip, the metering of the filmstrip, and the rewinding of the filmstrip, without independent mechanisms being required for the retraction of the metering apparatus. Such a metering apparatus should be simple in design and provides for a reduction of the number of mechanical components required within a camera.